This invention relates generally to gas turbine engines, and more specifically to igniter tubes used with gas turbine engine combustors.
Combustors are used to ignite fuel and air mixtures in gas turbine engines. Known combustors include at least one dome attached to a combustor liner that defines a combustion zone. More specifically, the combustor liner includes an inner and an outer liner that extend from the dome to a turbine nozzle. The liner is spaced radially inwardly from a combustor casing such that an inner and an outer passageway are defined between the respective inner and outer liner and the combustor casing.
At least some known gas turbine engines include an igniter tube that facilitates maintaining the igniter in alignment within the combustor. More specifically, the igniter extends through the igniter tube such that the igniter is maintained in alignment relative to the combustion chamber.
During operation, high pressure airflow is discharged from the compressor into the combustor where the airflow is mixed with fuel and ignited utilizing the igniters. Moreover, a portion of the airflow entering the combustor is channeled through the combustor outer passageway for cooling the outer liner, the igniters, and to facilitate diluting a main combustion zone within the combustion chamber. Because the igniters are bluff bodies, the airflow may separate and wakes may develop downstream from each igniter. As a result, a downstream side of the igniters and their respective igniter tubes are not as effectively cooled as an upstream side of the igniters and their respective igniter tubes which are each cooled using airflow that has not separated. Furthermore, as a result of the wakes generated by the igniters, circumferential temperature gradients may develop in the igniter tubes. Additionally, hot gases ingested into the igniter tube may result in relatively high temperatures, and temperature gradients, and/or stresses. Over time, continued operation with increased temperature gradients may induce potentially damaging thermal stresses into the combustor that exceed an ultimate strength of materials used in fabricating the igniter tubes. As a result, thermally induced transient and steady state stresses may cause low cycle fatigue (LCF) failure of the igniter tubes.
Because igniter tube replacement is a costly and time-consuming process, at least some known combustors increase a gap between the igniters and the igniter tubes to facilitate reducing thermal circumferential stresses induced within the igniter tubes. As a result of the gap, leakage passes from the passageways to the combustion chamber to provide a cooling effect for the igniter tubes adjacent the combustor liner. However, because such air is used in the combustion process, such gaps provide only intermittent cooling, and the igniter tubes may still require replacement.